There are many types of bearings that are used in various applications. Such bearings include journal bearings, roller bearings, spherical bearings and hourglass type bearings. In general, these bearings have an inner race that is disposed at least partially in an outer race. The inner race and outer race are movable relative to one another. There is an annular cavity between the inner race and the outer race that typically contains a lubricant. One well known problem with bearings is the ingress of debris and contaminants into the annular cavity which can cause premature failure of the bearings due to degradation of the lubrication. Moreover, operation of the bearing can cause the lubricant to inadvertently escape from the annular cavity.
In an effort to mitigate the aforementioned problems, seals have been positioned across the annular cavity to maintain the lubricant in the cavity and to prevent the ingress of debris into the annular cavity. However, during operation, such seals become dislodged from the bearing and fail to function. In addition, such seals have often been too flexible, thereby allowing the seal to glide over debris and sweep the debris into the annular cavity.
Referring to FIG. 8, typical hourglass roller bearings 500, include an inner member 510, for example a ball, surrounded by an outer member 512. A plurality of hourglass shaped rollers 515 are disposed between the inner member 510 and the outer member 512. The inner member 510 defines a radially outwardly facing convex bearing surface 520. The outer member 512 defines a first radially inwardly facing convex bearing surface 522A and a second radially inwardly facing convex bearing surface 522B. Each of the rollers 515 has a concave exterior surface 525 extending between axial end faces 525A and 525B of the roller 515.
When bearings are operated at high loads, the typical rollers 515 can experience a detrimental effect referred to as “end-stress.” As shown in FIG. 9, each of the rollers 515 has an effective length LE that extends between axially outermost portions of two high stress zones 535A and 535B. The concave exterior surface 525 of the typical hourglass roller 515 has a constant radius of curvature RC over the entire effective length LE. As shown in FIG. 10, typically the peak surface stress 550P occurs in the high stress zones 535A and 535B. The peak surface stress 550P causes accelerated wear of: 1) the radially outwardly facing convex bearing surface 520; 2) the first radially inwardly facing convex bearing surface 522A; 3) the second radially inwardly facing convex bearing surface 522B; and 4) the concave exterior surface 525 of the roller 515.
For example, FIG. 11 illustrates the outer member 512 having a line of surface distress 555 extending circumferential around a portion of the first radially inwardly facing convex bearing surface 522A, shown after testing (but before spalling) with a prior art hourglass shaped roller 515. FIGS. 12 and 13 illustrate the inner member 510 having lines of surface distress 555A, 555B, 555C and 555D at four locations where the high stress zones 535A and 535B of the prior art roller 515 contact the inner member 510, shown after testing (but before spalling). FIG. 14 illustrates additional wear in the form of spalling 566 on the radially outwardly facing convex bearing surface 520 of the inner member 510. FIG. 15 illustrates the prior art roller 515 having lines of burnished material 577 at an edge of the effective length LE that extends between the axially outermost portions of two high stress zones 535A and 535B.
Typical bearings include an inner member, for example a ball, surrounded by an outer member. A typical roller bearing includes a plurality of rollers disposed between the inner member and the outer member. A typical hourglass bearing includes a plurality of hourglass shaped rollers disposed between the inner member and the outer member. The inner member defines a radially outwardly facing convex bearing surface. The outer member defines a first radially inwardly facing convex bearing surface and a second radially inwardly facing convex bearing surface. Each of the rollers has a concave exterior surface extending between axial end faces and of the roller.
Corrosion is a major cause of bearing failure on aerospace structures. Corrosion can be due to moisture, salt spray, cleaning fluids, etc. There are several ways to prevent corrosion which include plating, such as Cadmium, on standard steel product, and the use of stainless steels. Stainless steels have differing corrosion resistance. CREN steels have much more corrosion protection than typical stainless steels used in bearings such as 440C (AMS 5630) Corrosion of the inner member, of the rollers and of the outer member impedes the ability of the bearing to function as intended. For example, a corroded bearing is less efficient than a bearing that has not undergone corrosion due to increased friction between contact surfaces as a result of said corrosion.
Bearings are typically used in aircraft wing flap arrangements. For example, U.S. Pat. No. 8,714,493 describes a trailing edge flap arrangement for an aircraft wing that includes a drop linkage arrangement that includes one or more bearings. The subject matter of U.S. Pat. No. 8,714,493 is incorporated by reference herein, in its entirety.